When great powers are on the rise, they have to decide how they will treat their declining peers. In the decades before 1914, Germany tried to supplant the United Kingdom as Europe’s leading power, whereas Russia allied itself with a weakened France. The United States attempted to prop up the United Kingdom’s great-power status after World War II but sought to weaken the Soviet Union as it crumbled in the 1980s. In this book, Shifrinson provides an elegant theory to explain these variations. A rising state tries to weaken its fading rival only if it concludes that the declining state will not be useful in checking other rival states and lacks the ability to strike back. Before 1914, for example, Germany improved its ties with a declining Austria-Hungary so as not to be bereft of allies as it faced the Triple Entente. Today, a rising China might not seek to weaken a declining United States if Washington can help Beijing restrain other great powers, such as Japan and Russia, or if the United States still poses a significant military threat.